WO2015033415A1

WO2015033415A1 - Valve seat

Info

Publication number: WO2015033415A1
Application number: PCT/JP2013/073895
Authority: WO
Inventors: 善夫小山; 松太郎原
Original assignee: Ｔｐｒ株式会社
Priority date: 2013-09-05
Filing date: 2013-09-05
Publication date: 2015-03-12
Also published as: BR112015026887A2; US9556761B2; EP2982836B1; CN105102776B; EP2982836A1; US10036287B2; US20160333456A1; JP5856359B2; CN105102776A; JPWO2015033415A1; US20160201527A1; BR112015026887A8; EP2982836A4; KR20160014101A; BR112015026887B1; KR101600907B1

Abstract

A valve seat which exhibits excellent radial crushing strength and excellent abrasion resistance is provided. This valve seat is composed of an oxidation-treated iron-base sintered alloy. This oxidation-treated iron-based sintered alloy is prepared by subjecting an iron-base sintered alloy which contains 4 to 15 mass% of Co particles and hard particles to oxidation treatment, and thereby forming an oxide component which comprises both triiron tetraoxide (Fe₃O₄) and cobalt oxide (CoO) as main components on the surface of the iron-base sintered alloy and in the inside thereof. The hard particles contain at least one compound selected from among intermetallic compounds, carbides, silicides, nitrides and borides, each of which contains one or more elements selected from among group 4a to 6a elements of the periodic table. Further, the hard particles exhibit a hardness of 600 to 1600HV. At a stage prior to the application of the valve seat to a cylinder head, the oxidation-treated iron-base sintered alloy exhibits an area fraction of the oxide component of 5 to 25% in a cross section of the oxidation-treated iron-base sintered alloy.

Description

Valve seat

The present invention relates to a valve seat used for an internal combustion engine.

The valve seat is a part that serves as a valve seat for the intake valve and the exhaust valve, and is a part that is in contact with the valve (valve) to keep the combustion chamber airtight.

The valve seat is (1) an airtight holding function for preventing compressed gas and combustion gas from leaking to the manifold, (2) a heat conduction function for releasing the heat of the valve to the cylinder head side, and (3) when the valve is seated There are demands for functions such as strength that can withstand valve collisions, and (4) wear resistance that resists wear even in high heat and high load environments.

Also, the required characteristics of the valve seat include (5) less aggressiveness to the counterpart valve, (6) reasonable price, and (7) easy cutting during processing.

Therefore, an iron-based sintered alloy is used for the valve seat in order to satisfy the functions and characteristics described above.

For example, in Patent Document 1, an oxide mainly composed of iron trioxide is formed on the surface and inside of an iron-based sintered alloy by oxidation treatment, and in a state before being attached to the cylinder head, A valve seat is disclosed in which the area ratio of an oxide mainly composed of triiron tetroxide in the cross section of the base sintered alloy is 5 to 20%.

JP2013-113220A

In recent years, the operating conditions of internal combustion engines have become stricter, and higher wear resistance and crushing strength are required for valve seats attached to cylinder heads of internal combustion engines.

Therefore, an object of the present invention is to provide a valve seat excellent in wear resistance and crushing strength.

As a result of various studies, the present inventors have found that a valve seat excellent in wear resistance and crushing strength can be obtained by oxidizing iron-based sintered alloy containing Co particles, and the above object is achieved. It came to achieve.

That is, the present invention is a valve seat attached to a cylinder head of an internal combustion engine, wherein the valve seat includes 4 to 15% by mass of Co particles and one or more elements selected from Group 4a to 6a of the periodic table. An iron-based sintered alloy containing hard particles having a hardness of 600 to 1600 HV containing at least one compound selected from the group consisting of intermetallic compounds, carbides, silicides, nitrides and borides, is oxidized, It is composed of an oxidized iron-based sintered alloy in which an oxide mainly composed of triiron tetroxide (Fe ₃ O ₄ ) and cobalt oxide (CoO) is formed on the surface and inside of the sintered alloy, and the oxidized iron The base sintered alloy is characterized in that the area ratio of the oxide in the cross section of the oxidized iron-based sintered alloy is 5 to 25% before being attached to the cylinder head.

According to the valve seat of the present invention, it is composed of an oxidized iron-based sintered alloy obtained by oxidizing iron-based sintered alloy containing 4 to 15% by mass of Co particles and the hard particles. By the treatment, Co particles generate cobalt oxide (CoO), and the crushing strength is improved, and the action of the self-lubricant (the action of suppressing wear of the valve seat or the valve of the counterpart material) by the cobalt oxide (CoO). And wear resistance is improved. Further, the crushing strength is improved by the effect of adding hard particles. In addition, since an oxide mainly composed of triiron tetroxide (Fe ₃ O ₄ ) and cobalt oxide (CoO) is formed on the surface and inside, it is previously formed on the surface of the valve seat during operation. Oxide tends to be formed on the contact surface with the valve starting from the oxide. By forming an oxide on the contact surface with the valve, metal contact between the valve and the valve seat is suppressed, and the wear resistance of the valve seat is improved. By setting the area ratio of the oxide in the cross section of the oxidized iron-based sintered alloy to 5 to 25%, the wear resistance can be improved while maintaining the crushing strength.

In the present invention, the Co particles preferably have an average particle size of 10 to 40 μm. According to this aspect, the dispersibility of the Co particles in the iron-based sintered alloy is good, and variations in wear resistance and crushing strength can be suppressed.

In the present invention, the hard particles are preferably Co-based alloy particles containing 28 to 38% by mass of Co and containing carbides. According to this aspect, since the Co oxide is generated from the Co component diffused from the hard particles during the oxidation treatment of the iron-based sintered alloy, the wear resistance and the crushing strength of the valve seat can be further increased.

In the present invention, the iron-based sintered alloy preferably has an area ratio of the hard particles in a cross section of the iron-based sintered alloy of 5 to 45%. According to this aspect, the plastic flow of the iron-based sintered alloy is suppressed, and the wear resistance of the valve seat can be further improved.

In the present invention, the iron-based sintered alloy preferably further contains a solid lubricant. The solid lubricant preferably has an average particle size of 1 to 10 μm. According to this aspect, the wear resistance of the valve seat can be further improved.

According to the present invention, it is possible to provide a valve seat having excellent crushing strength and wear resistance.

3 shows the results of an abrasion resistance test of valve seats obtained by oxidizing iron-based sintered alloys having compositions 1-1 to 1-4. 3 shows the results of an abrasion resistance test of a valve seat obtained by oxidizing iron-based sintered alloys having compositions 2-1 to 2-4. 3 is a result of a crushing strength test of a valve seat obtained by oxidizing iron-based sintered alloys having compositions 1-1 to 1-4. 3 is a result of a crushing strength test of a valve seat obtained by oxidizing iron-based sintered alloys having compositions 2-1 to 2-4. 6 is an oxygen map of a valve seat of Test Example 2. It is the structure | tissue photograph (500 times) of the valve seat of the composition 3-3 by a metal microscope. It is the structure | tissue photograph (500 times) by the scanning electron microscope of the valve seat. It is Co map by the energy dispersive X-ray analyzer (EDX) of the valve seat corresponding to the structure | tissue photograph of FIG. It is O map by the energy dispersive X-ray-analysis apparatus (EDX) of the valve seat corresponding to the structure | tissue photograph of FIG. It is a Fe map by the energy dispersive X-ray analyzer (EDX) of the valve seat corresponding to the structure photograph of FIG. 5 shows the results of a wear resistance test and a crushing strength test of the valve seat of Test Example 2. It is the schematic of a valve seat abrasion tester.

The valve seat of the present invention has a hardness containing Co particles and at least one compound of an intermetallic compound, carbide, silicide, nitride, and boride containing one or more elements selected from Group 4a to 6a of the periodic table. An iron-based sintered alloy containing hard particles of 600 to 1600 HV is oxidized, and iron trioxide (Fe ₃ O ₄ ) and cobalt oxide (CoO) are added to the surface and inside of the iron-based sintered alloy. It is composed of an oxidized iron-based sintered alloy in which a main oxide is formed.

In the present invention, the valve seat needs to have an area ratio of the oxide of 5 to 25% in the cross section of the oxidized iron-based sintered alloy before being attached to the cylinder head. 20% is more preferable. When the area ratio of the oxide is in the above range, a valve seat excellent in crushing strength and wear resistance can be obtained. When the area ratio of the oxide exceeds 25%, the crushing strength is lowered, and the oxide is easily damaged by an impact when the valve is seated on the valve seat. When the area ratio of the oxide is less than 5%, the wear resistance is poor. In order to adjust the area ratio of the oxide to 5 to 25%, there is a method of adjusting the oxidation treatment time during the oxidation treatment.

In the present invention, as shown in Examples described later, an arbitrary cross section of a valve seat (oxidized iron-based sintered alloy) is observed with a scanning electron microscope, and the observed image is converted into an energy dispersive X-ray analyzer ( The oxygen map is obtained using the oxygen map of EDX), the luminance of the obtained oxygen map data is binarized to obtain an area ratio of luminance of 5 or more, and an average value of N = 3 locations / piece × 10 points The area ratio of the oxide mainly composed of iron trioxide (Fe ₃ O ₄ ) and cobalt oxide (CoO) was used.

In the present invention, the content of Co particles in the iron-based sintered alloy before the oxidation treatment is 4 to 15% by mass, preferably 6 to 13% by mass. By oxidizing the iron-based sintered alloy containing Co particles, cobalt oxide (CoO) is generated. The produced cobalt oxide (CoO) acts as a self-lubricating material, and can suppress wear of the valve seat and the counterpart valve. For this reason, the wear resistance of the valve seat is improved. Moreover, the crushing strength of the valve seat is also improved. When the content of Co particles is less than 4% by mass, the crushing strength and wear resistance of the valve seat tend to be insufficient. Increasing the content of Co particles improves the crushing strength and wear resistance, but if it exceeds 15%, it becomes too hard and tends to increase the wear of the counterpart material. In addition, high costs are invited.

The purity of the Co particles (Co content) is preferably 99% by mass or more.

In the present invention, the area ratio of the hard particles in the cross section of the iron-based sintered alloy before the oxidation treatment is preferably 5 to 45%, more preferably 15 to 40%. By containing hard particles in the iron-based sintered alloy, plastic flow of the valve seat can be suppressed, and wear resistance can be further improved. If the area ratio of the hard particles exceeds 45%, the productivity is inferior. Furthermore, the density of the iron-based sintered alloy tends to decrease and the crushing strength tends to decrease. When the area ratio of the hard particles is less than 5%, the effect of adding the hard particles may not be sufficiently obtained.

In addition, in this invention, as shown in the Example mentioned later, the arbitrary cross sections of the iron-based sintered alloy before oxidation treatment are observed at 200 times using an optical microscope or an electron microscope, and a cross-sectional structure in the range of 1 mm × 1 mm. The area of the hard particle portion of the photograph was traced on a graph paper to determine the area, and the average value of the four measured values was defined as the area ratio of the hard particles.

In the present invention, the content of hard particles in the iron-based sintered alloy before the oxidation treatment is preferably 5 to 45% by mass, and more preferably 15 to 40% by mass. By increasing the content of the hard particles, the area ratio of the hard particles in the cross section of the iron-based sintered alloy can be increased. By setting the hard particle content to 5 to 45% by mass, the area ratio of the hard particles in the cross section of the iron-based sintered alloy can be set to 5 to 45%.

In the present invention, the hardness of the hard particles is preferably from 600 to 1600 HV, more preferably from 650 to 1400 HV. If the hardness of the hard particles is less than 600 HV, the wear resistance of the valve seat tends to be insufficient. When the hardness of the hard particles exceeds 1600 HV, wear of the counterpart valve tends to increase. In the present invention, the hardness of the hard particles means a value measured according to JIS Z2244 “Vickers hardness test-test method”.

Specific examples of hard particles include intermetallic compound particles such as Fe—Mo (ferromolybdenum), Fe—Cr (ferrochromium), Co—Mo—Cr, carbides such as Cr and Mo, silicides, nitrides, and borides. Fe-based alloy particles in which one or more types selected from the above are dispersed, carbides such as Cr and Mo, Co-based alloy particles in which one or more types selected from silicides, nitrides and borides are dispersed, carbides such as Cr and Mo, Ni-based alloy particles in which one or more selected from silicides, nitrides and borides are dispersed may be mentioned. Among these, Co-based alloy particles containing 28 to 38% by mass of Co and containing carbide are preferably used. By using Co-based alloy particles as the hard particles, Co oxide is generated from the Co component diffused from the hard particles during the oxidation treatment of the iron-based sintered alloy, making it easier to obtain the effect of a self-lubricant. , Wear resistance is improved. Furthermore, the crushing strength can be further increased. When Co-based alloy particles are used as the hard particles, the Co content in the valve seat (the total of Co particles and Co in the hard particles) is preferably 5 to 32% by mass, and preferably 10 to 28% by mass. More preferred.

The valve seat of the present invention may further contain a solid lubricant. By containing the solid lubricant, the wear resistance of the valve seat is improved. The solid lubricant is not particularly limited. For example, calcium fluoride, manganese sulfide, molybdenum sulfide, tungsten sulfide, chromium sulfide, enstatite, talc, boron nitride, and the like can be given.

The content of the solid lubricant in the valve seat is preferably 0 to 5% by mass, more preferably 0 to 3% by mass. Since the crushing strength tends to decrease as the solid lubricant content increases, the upper limit is preferably 5% by mass.

In the present invention, the valve seat may further contain other additive elements other than Co, hard particles and solid lubricant. Other additive elements include C, Cu, Ni, Cr, Mo, P, and Mn.

The valve seat of the present invention is excellent in crushing strength and wear resistance, and can be preferably used as a valve seat attached to a contact surface of a cylinder head of an internal combustion engine such as a gas engine or an alcohol engine.

The valve seat of the present invention may be composed of only the oxidized iron-based sintered alloy. The portion corresponding to the contact surface with the valve is made of the above-mentioned oxidized iron-based sintered alloy, and the portion corresponding to the cylinder head side seating surface is made of an inexpensive iron-based sintered alloy that has been used conventionally. It may be a laminated body with other materials. By using a laminated body, the material cost can be reduced.

The manufacturing method of the valve seat of the present invention is not particularly limited, but can be manufactured by the following method, for example.

First, as raw materials for iron-based sintered alloys, pure iron powder, Cr steel powder, Mn steel powder, MnCr steel, CrMo steel powder, NiCr steel powder, NiCrMo steel powder, tool steel powder, high speed steel powder, Co alloy steel To the raw iron powder such as powder and Ni steel powder, Co particles, hard particles, and other optional elements, solid lubricant, etc. are added and mixed as optional components.

The mixing ratio of each raw material is not particularly limited. Examples thereof include 35 to 91% by mass of raw iron powder, 5 to 45% by mass of hard particles, 4 to 15% by mass of Co particles, and 0 to 5% by mass of a solid lubricant. By increasing the mixing ratio of the hard particles, the area ratio of the hard particles in the cross section of the iron-based sintered alloy can be increased. For example, by setting the mixing ratio of the hard particles to 5 to 45% by mass, the area ratio of the hard particles in the cross section of the iron-based sintered alloy can be set to 5 to 45%.

The average particle size of the raw iron powder is preferably 40 to 150 μm. If the average particle size of the raw iron powder is less than 40 μm, the density of the green compact varies due to the decrease in fluidity, and the pressure ring strength of the valve seat tends to vary. When the average particle diameter of the raw iron powder exceeds 150 μm, the gap between the powders becomes large, the density of the green compact decreases, and the crushing strength of the valve seat tends to decrease. In the present invention, the value of the average particle diameter means a value measured with a laser diffraction / scattering particle size distribution measuring apparatus.

The average particle size of the hard particles is preferably 20 to 70 μm. When the average particle size of the hard particles is less than 20 μm, the wear resistance of the valve seat tends to be lowered. If the average particle size of the hard particles exceeds 70 μm, the hard particles in the iron-based sintered alloy tend to be sparse, difficult to disperse uniformly, and the wear resistance of the valve seat tends to vary.

The average particle size of the Co particles is preferably 10 to 40 μm. When the average particle size of the Co particles is less than 10 μm, Co aggregates and is difficult to disperse uniformly in the iron-based sintered alloy, and the wear resistance of the valve seat tends to vary. If the average particle size of the Co particles exceeds 40 μm, Co in the iron-based sintered alloy tends to be sparse, difficult to disperse uniformly, and the wear resistance of the valve seat tends to vary.

The average particle size of the solid lubricant is preferably 1 to 10 μm. When the average particle size of the solid lubricant is less than 1 μm, the solid lubricant aggregates and is difficult to uniformly disperse in the iron-based sintered alloy, and the wear resistance of the valve seat tends to vary. If the average particle size of the solid lubricant exceeds 10 μm, the compressibility is hindered during molding, and the density of the green compact tends to decrease, and the crushing strength of the valve seat tends to decrease.

Other additive elements may be added in the form of oxides, carbonates, elemental elements, alloys, and the like.

Next, the mixture of raw material powders is filled in a mold and compression molded by a molding press to produce a green compact.

Next, the green compact is fired to produce a sintered body (iron-based sintered alloy). Firing conditions are preferably 1050 to 1200 ° C. and 0.2 to 1.5 hours.

Next, the iron-based sintered alloy is oxidized. The oxidation treatment is preferably a steam treatment from the viewpoint of the stability of the oxidizing atmosphere. However, the surface of the iron-based sintered alloy, such as a method of oxidizing in an oxidizing atmosphere in a heating furnace, is formed on the surface of the iron-based sintered alloy (Fe ₃ O ₄₎ and particularly limited as long as it is a method capable of producing cobalt oxide (CoO) is not.

In the present invention, the oxidation treatment is performed so that the area ratio of the oxide containing triiron tetroxide (Fe ₃ O ₄ ) and cobalt oxide (CoO) is 5 to 25% in the cross section of the iron-based sintered alloy. . When the oxidation treatment time is set long, the area ratio of the oxide increases, and when it is set short, the area ratio of the oxide decreases. The oxidation treatment time may be adjusted as appropriate so that the oxide area ratio is 5 to 25%. To explain with a specific example, the area ratio of the oxide can be made 5 to 25% by performing steam treatment at 500 to 600 ° C. for 0.2 to 5 hours.

Next, the valve seat is obtained by polishing and cutting the iron-based sintered alloy that has been subjected to the oxidation treatment.

<Measurement method>
-Measurement of area ratio of oxide A part of the cross section of the valve seat was extracted with a scanning electron microscope, and obtained by the following procedure using an oxygen map of an energy dispersive X-ray analyzer (EDX).

(1) The cut valve seat was embedded in a resin, and the sample was polished using diamond abrasive grains.

(2) The scanning electron microscope was “VE8800” (trade name, manufactured by Keyence), and observed at an acceleration voltage of 15 kV and a magnification of 500 times.

(3) EDX uses "INCA 250 XTK" (trade name, manufactured by Oxford Instruments), and EDX software uses "The Microanalysis Suite-Issure 18d version 4.15" (manufactured by Oxford Instruments) It was used.

(4) An electron microscope image was taken into EDX software with an image resolution of 512 × 384 pixels.

(5) X-ray collection was performed 10 times with a dwell time of 100 μs / pixel, with a process time scale set 6, a spectral range of 0 to 20 keV, a channel number of 2 k, and a collection count rate of 30%.

(6) In order to enhance the contrast of the obtained oxygen map, a process of combining 2 × 2 pixels into one pixel was performed, and the X-ray intensity was quadrupled.

(7) After the processing of (6), the area calculation function of EDX software is used to binarize the brightness of the oxygen map data to obtain an area ratio of brightness 5 or higher, and N = 3 places / piece × 10 points average value Was the area ratio of the oxide.

・ Measurement of the area ratio of hard particles The cross section of the iron-based sintered alloy was observed at 200 times using an optical microscope or an electron microscope, and the hard particle portion of the cross-sectional structure photograph in the range of 1 mm × 1 mm was traced on graph paper. The area was calculated, and the average value of the four measured values was defined as the area ratio of the hard particles.

-Wear resistance test The valve seat 3 was attached to the valve seat abrasion tester shown in FIG. That is, the valve seat wear tester is configured such that the face surface of the valve 4 is brought into contact with the valve seat 3 fitted in the seat holder 2 at the upper end of the frame 1 by the spring 5. The valve 4 is lifted upward via a rod 8 by a camshaft 7 that is rotated by an electric motor 6, and then returned by a spring 5, thereby hitting the valve seat 3. The valve 4 is heated by the gas burner 9 and the temperature of the valve seat 3 is measured by the thermocouple 10 to control the temperature. When the valve 4 is heated, the combustion state of the gas burner is set to complete combustion so that no oxide film is formed on the surface. The valve 4, the spring 5, the camshaft 7 and the like use actual engine parts. And the abrasion resistance test was done on the conditions shown in Table 1.

-Crushing strength test Measurement was performed according to JIS Z2507 "Testing method of crushing strength of sintered oil-impregnated bearings".

-Hardness measurement Measured according to JIS Z2245 "Rockwell hardness test-test method".

-Density measurement Measured according to JIS Z2501 "Sintered metal material-Test method for density, oil content and open porosity".

(Test Example 1)
Fe powder, hard particles (Co-based alloy particles), Co particles, and solid lubricant (manganese sulfide) were mixed in the proportions shown in Tables 2 and 3 and filled into a mold, and then compression molded by a molding press. The obtained green compact was fired at 1120 ° C. for 0.5 hours to obtain an iron-based sintered alloy.

Next, this iron-based sintered alloy is subjected to an oxidation treatment by changing the conditions in a temperature range of 500 to 600 ° C. and in a range of a treatment time of 0.2 to 5 hours, thereby oxidizing the iron-based sintered bond. An oxide mainly composed of triiron tetroxide (Fe ₃ O ₄ ) and cobalt oxide (CoO) was formed on the surface and inside of gold by changing the area ratio. Thus, valve seats (oxidized iron-based sintered alloys) having oxide area ratios of 0%, 3%, 5%, 10%, 15%, 20%, and 25% were obtained.

The wear resistance test and the crushing strength test were performed on each valve seat. The results are shown in FIGS. FIG. 1 shows the results of an abrasion resistance test of valve seats obtained by oxidizing iron-based sintered alloys having compositions 1-1 to 1-4. FIG. 2 shows the results of a wear resistance test of valve seats obtained by oxidizing iron-based sintered alloys having compositions 2-1 to 2-4. FIG. 3 shows the results of a crushing strength test of valve seats obtained by oxidizing iron-based sintered alloys having compositions 1-1 to 1-4. FIG. 4 shows the results of a crushing strength test of valve seats obtained by oxidizing iron-based sintered alloys having compositions 2-1 to 2-4. The wear amount ratio was expressed as a relative value when the addition amount of Co particles was 0% by mass and the wear amount of a valve seat that was not subjected to oxidation treatment was 100. The crushing strength ratio was expressed as a relative value when the crushing strength of an iron-based sintered alloy in which the addition amount of Co particles was 0% by mass and the oxidation treatment was not performed was 100.

As shown in FIGS. 1 to 4, the wear resistance and the crushing strength improved as the oxide area increased. The effect increases remarkably when the oxide area is 5% or more, but it is understood that the increase in the effect decreases when it exceeds 20%. Moreover, the wear resistance and the crushing strength were improved by adding Co particles to the iron-based sintered alloy.

(Test Example 2)
Fe powder, hard particles (Co-based alloy particles), Co particles, and solid lubricant (manganese sulfide) were mixed at a ratio shown in Table 4 and filled in a mold, and then compression molded by a molding press. The obtained green compact was fired at 1120 ° C. for 0.5 hours to obtain an iron-based sintered alloy.

Next, this iron-based sintered alloy is oxidized by steaming at 550 ° C. for 1 hour, and iron trioxide (Fe ₃ O ₄ ) and oxidized are formed on the surface and inside of the iron-based sintered alloy. A valve seat (oxidized iron-based sintered alloy) was obtained by generating an oxide mainly composed of cobalt (CoO) so as to have an area ratio of about 10%.

Fig. 5 shows the oxygen map of the valve seat. FIG. 6 shows a structure photograph (500 times) of a valve seat having a composition 3-3 (the addition amount of Co particles is 8% by mass) by a metallographic microscope. In FIG. 7, the structure | tissue photograph (500 times) of the valve seat by the scanning electron microscope is shown. FIGS. 8 to 10 show the Co map, O map, and Fe map of the valve seat by the energy dispersive X-ray analyzer (EDX) corresponding to the structure photograph of FIG. 6 to 10, a region where the Co oxide and the Fe-based oxide are present is surrounded by a solid line, and a region where the hard particles are present is surrounded by a broken line.

6 to 10, it can be seen that oxide (CoO) is generated from the Co particles added to the iron-based sintered alloy by the oxidation treatment. It can also be seen that oxide (CoO) is also generated from the Co component diffused from the hard particles (Co—Mo—Cr).

Further, the obtained valve seat was subjected to an abrasion resistance test and a crushing strength test. The results are shown in FIG. The wear amount ratio is shown as a relative value when the wear amount of composition 3-1 (addition of Co particles is 0% by mass) is defined as 100. The crushing strength ratio was expressed as a relative value when the crushing strength of the composition 3-1 (addition of Co particles was 0% by mass) was 100.

As shown in FIG. 11, the wear resistance and the crushing strength were improved by increasing the amount of Co particles added.

Claims

A valve seat attached to a cylinder head of an internal combustion engine,
The valve seat comprises at least one compound of intermetallic compounds, carbides, silicides, nitrides and borides containing 4 to 15% by mass of Co particles and one or more elements selected from groups 4a to 6a of the periodic table An iron-based sintered alloy containing hard particles having a hardness of 600 to 1600 HV including oxidization is oxidized, and triiron tetroxide (Fe 3 O 4 ) and oxidation are formed on the surface and inside of the iron-based sintered alloy. It is composed of an oxidized iron-based sintered alloy in which an oxide mainly composed of cobalt (CoO) is formed,
The oxidized iron-based sintered alloy is characterized in that an area ratio of the oxide in a cross section of the oxidized iron-based sintered alloy is 5 to 25% before being mounted on a cylinder head. Valve seat.
The valve seat according to claim 1, wherein the Co particles have an average particle size of 10 to 40 µm.
The valve seat according to claim 1 or 2, wherein the hard particles are Co-based alloy particles containing 28 to 38% by mass of Co and containing carbides.
The valve seat according to any one of claims 1 to 3, wherein the iron-based sintered alloy has an area ratio of the hard particles in a cross section of the iron-based sintered alloy of 5 to 45%.
The valve seat according to any one of claims 1 to 4, wherein the iron-based sintered alloy further contains a solid lubricant.
6. The valve seat according to claim 5, wherein the solid lubricant has an average particle diameter of 1 to 10 μm.